Method for the monitoring of a degree of coking at seals by a gas generator shaft

ABSTRACT

The invention relates to a method (1000) for monitoring a degree of coking at dynamic seals of a turbine engine comprising: a gas generator including a rotary shaft and an injection wheel mounted on the shaft; a fuel injection manifold designed to convey fuel to the injection wheel; and dynamic seals designed to provide a seal between the injection wheel and the fuel injection manifold. The method is characterised in that it comprises steps consisting in: measuring (1100) the rotation speed of the gas generator shaft during a turbine engine autorotation phase, and determining (1200) a degree of coking at the dynamic seals, based on changes in the measured rotation speed over time. The invention also relates to a turbine engine equipped with a monitoring system.

FIELD OF THE INVENTION

The field of the invention is that of the monitoring of the degree of coking at dynamic seals in a turbine engine, and of turbine engines equipped with systems allowing said monitoring.

STATE OF THE ART

With reference to FIG. 1a , certain turbine engines 1, like for example turbomotors, comprise a gas generator 10 comprising a rotary shaft 11 on which is mounted an injection wheel 12, which is therefore itself rotary.

The injection wheel has a plurality of orifices which open into a combustion chamber 30. In this way, the injection wheel, during its rotation, sprays fuel by centrifugation into the combustion chamber.

With reference to FIG. 1b , the turbine engine also comprises an injection manifold 20, which is a fixed axisymmetrical part mounted around the shaft 11 of the gas generator 10.

The injection manifold conveys fuel as far as the injection wheel. The fuel flows in an internal conduit 21 of the injection manifold, and opens into a cavity 22 before penetrating into the injection wheel.

In order to ensure the seal between the injection wheel and the manifold, a plurality of dynamic seals such as labyrinth seals 23 are provided.

Now, it often happens that coke forms in the grooves of these seals, consequently causing the occurrence of friction between the injection wheel and the injection manifold. The friction may be worsened until it causes complete blocking of the shaft of the gas generator; it is then no longer possible to start the engine.

In the case of difficulties with starting, the operators carry out operations for searching faults described in a maintenance manual of the turbine engine. These searching operations are generally long and not very efficient, since sometimes a significant time has to be spent before the cause of the starting difficulties is detected, in this case, coking at the dynamic seals (indeed, many other causes may be contemplated).

Further, these searching operations imply unplanned unavailability of the turbine engine, and therefore of the aircraft in which it is installed, which may further require cancellation of one or several planned flight missions. These operations therefore represent a significant cost.

No alternative method allowing anticipation of the blocking of the shaft of the gas generator because of coking at dynamic seals, and thereby giving the possibility of avoiding fault-searching operations, has ever been proposed.

Therefore there exists a need for a method for monitoring a degree of coking at the dynamic seals.

PRESENTATION OF THE INVENTION

The object of the invention is to find a remedy to the problem presented herein before, by proposing a method for monitoring a degree of coking at the dynamic seals of a turbine engine.

Another object of the invention is to be able to monitor this degree of coking upon using the turbine engine, without imposing any unavailability of the turbine engine.

In this respect, the object of the invention is a method for monitoring a degree of coking at the dynamic seals of a turbine engine comprising:

-   -   a gas generator comprising a rotary shaft and an injection wheel         mounted on said shaft, the injection wheel being adapted for         spraying fuel by centrifugation, and     -   an injection manifold, adapted for conveying fuel as far as the         injection wheel,     -   dynamic seals adapted for ensuring a seal between the injection         wheel and the injection manifold,         the method being characterized in that it comprises the steps:     -   measuring during a self-rotation phase of the turbine engine,         the speed of rotation of the gas generator shaft, and     -   determining from the time-dependent change of the thereby         measured speed of rotation, a degree of coking at the dynamic         seals.

Advantageously, but optionally, the method according to the invention may further comprise at least one of the following features:

-   -   the step for determining the degree of coking at the dynamic         seals comprises measurement of the deceleration of the gas         generator shaft between two speeds of rotation of the shaft.     -   the measurement of deceleration is conducted between a first         speed of rotation comprised between 1,000 and 2,500 revolutions         per minute, preferably equal to 1,000 revolutions per minute and         a second speed of rotation comprised between 500 and 1,000         revolutions per minute preferably equal to 700 revolutions per         minute.     -   the determination of the degree of coking at the dynamic seals         comprises one of steps from among the following group:         -   comparing the deceleration of the gas generator shaft with a             predetermined threshold,         -   determining a difference between the measured deceleration             and an initial deceleration of the turbine engine between             the same speeds of rotation of the shaft, and comparing the             difference with a predetermined threshold, and         -   determining, from previous measurements of the deceleration,             a change rate of said deceleration depending on the use of             the turbine engine, and comparing said change rate with a             predetermined threshold.     -   The method is applied in a turbine engine further comprising a         starter and comprises the steps:         -   measuring, during a phase for initiating rotation of the gas             generator shaft by the starter upon starting the turbine             engine, a current flowing though the starter and a voltage             on the terminals of the starter,         -   determining from the measured current and voltage, a             representative datum of a resistive torque of the shaft of             the gas generator,     -   the step for determining a degree of coking at the dynamic seals         is carried out from the time-dependent change of the speed of         rotation of the shaft of the gas generator and from the value or         time-dependent change of the representative datum of a resistive         torque depending on the use of the turbine engine.

The object of the invention is also a system for monitoring a degree of coking at the dynamic seals of a turbine engine comprising:

-   -   a gas generator, comprising a rotary shaft and an injection         wheel mounted on said shaft, the wheel being adapted for         spraying fuel by centrifugation,     -   an injection manifold, adapted for conveying fuel as far as the         injection wheel, and     -   dynamic seals, adapted for ensuring a seal between the injection         wheel and the injection manifold,         the monitoring system being adapted for applying the method         according to the preceding presentation, and comprising:     -   at least one sensor for the speed of rotation of the shaft of         the gas generator, adapted so as to carry out acquisitions at a         frequency greater than or equal to 2 Hz, and     -   a processing unit, including a memory and suitable processing         means for the measurements of speed of rotation for determining         a degree of coking at the dynamic seals.

The monitoring system according to the invention, when set up in a turbine engine further comprising a starter, may further comprise additionally at least one device for measuring a voltage on the starter terminals and current flowing through it, said measuring device being adapted for acquiring voltage and current measurements at a frequency greater than or equal to 10 Hz.

The object of the invention is also a turbine engine comprising:

-   -   a gas generator, comprising a rotary shaft and an injection         wheel mounted on said shaft, the wheel being adapted for         spraying fuel by centrifugation,     -   an injection manifold adapted for conveying fuel as far as the         injection wheel, and     -   dynamic seals, adapted for ensuring a seal between the injection         wheel and the injection manifold,         the turbine engine being characterized in that it further         comprises a monitoring system according to the preceding         description.

The thereby proposed monitoring method gives the possibility of evaluating a degree of coking at the dynamic seals of a turbine engine, and of detecting a critical stage before impossibility of starting the turbine engine.

This allows if required planning maintenance for cleaning or replacing the dynamic seals.

DESCRIPTION OF THE FIGURES

Other features, objects and advantages of the invention will become apparent from the description which follows, which is purely illustrative and non-limiting, and which should be read with reference to the appended drawings wherein:

FIGS. 1a and 1b , already described, schematically illustrate the principle of operation of a turbine engine equipped with an injection wheel,

FIGS. 2a and 2b illustrate the main steps of a monitoring method according to two embodiments of the invention.

FIG. 3a illustrates the period for decelerating the shaft of the gas generator for different degrees of use of the turbine engine.

FIG. 3b illustrates the time-dependent change of a deceleration of a shaft of a gas generator depending on the use of the turbine engine.

FIG. 4 illustrates the time-dependent change of a datum representative of the resistive torque of a gas generator shaft depending on the use of the turbine engine.

DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT OF THE INVENTION

In FIGS. 2a and 2b two embodiments of a method for monitoring the coking at the dynamic seals of a turbine engine are illustrated.

Like in the illustration of FIG. 1a , the turbine engine 1 which may be a turbomotor, comprises a gas generator 10, comprising a rotary shaft 11, driving into rotation an injection wheel 12 mounted on the latter.

The turbine engine further comprises a fixed injection manifold 20, which is an axisymmetrical part around the shaft of the gas generator. The injection manifold 20 comprises at least one internal duct 21 which opens into a circumferential cavity 22.

The turbine engine also comprises a combustion chamber 30 in which takes place the ignition of the fuel for propelling the aircraft in which is mounted the turbine engine.

The injection wheel 12 comprises radial internal channels 13 which open on one side into the circumferential cavity 22 and on the other side into the combustion chamber 30.

The fuel is conveyed through the injection manifold as far as the cavity 22, where it is then driven into the injection wheel 12 through opening orifices from the channels 13 laid out in the latter. The fuel is then sprayed into the combustion chamber by centrifugation resulting from the rotary movement of the injection wheel.

In order to ensure the seal between the movable injection wheel 12 and the fixed injection manifold 20, the turbine engine further comprises a plurality of dynamic seals 23, advantageously of the labyrinth seal type.

Thus, the fuel present in the cavity 22 does not leak into the other sectors of the turbine engine.

The turbine engine further comprises a starter 40 which gives the possibility of driving into rotation the shaft of the gas generator during a starting phase of the turbine engine.

In particular, the starting phase comprises a first period which lasts for about 4 seconds, during which the combustion chamber is not ignited and the shaft of the gas generator is driven into rotation exclusively by the starter. This phase is subsequently called “initiation phase of the rotation of the shaft of the gas generator”.

The starting phase then comprises a second period, during which the combustion chamber is ignited, and the shaft of the gas generator accelerates under the simultaneous action of the starter and of the thermal power of the turbine engine.

The turbine engine finally comprises a system 50 for monitoring the degree of coking at the dynamic seals.

This system comprises a processing unit 51, which is connected to one or several sensors, and which is adapted for recovering the measurements of the sensors and for processing them in a way which is explained hereafter for inferring therefrom a degree of coking at the dynamic seals.

The processing unit 51 may be integrated to the turbine engine or alternatively be separated therefrom, for example by being mounted in the aircraft or in a monitoring central system on the ground. If necessary, communication of the data between the sensor(s) and the processing unit may be achieved during the use of the turbine engine by wireless communication or else be achieved occasionally during a stopping phase of the turbine engine, by recovering the data on the sensors and loading them into the processing unit.

The processing unit advantageously comprises a memory 52 giving the possibility of storing the measurements made during the previous uses of the turbine engine, and means for processing data like a processor 53.

The monitoring system also comprises, according to a first embodiment corresponding to the method of FIG. 2a , a sensor 54 of the speed of the shaft of the gas generator, which is adapted for measuring said speed at a frequency greater than or equal to 1 Hz, preferably greater than or equal to 2 Hz.

According to a second embodiment corresponding to the method of FIG. 2 b, the monitoring system 50 comprises a device 55 for measuring a voltage on the starter 40 terminals and a current flowing through it, which is adapted for measuring these data at a frequency greater than or equal to 2 Hz, preferably greater than or equal to 10 Hz.

Both indicators used for monitoring the degree of coking at the seals may be combined for corroborating their results, the monitoring system advantageously comprises both a sensor 54 for the speed of rotation of the shaft and a device 55 for measuring the voltage on the terminals of the starter and the current flowing through it.

The monitoring system may also comprise other sensors giving the possibility of providing additional information to the processing unit for inferring therefrom a more accurate degree of coking at the seals.

Monitoring a Degree of Coking at Dynamic Seals by the Speed of Rotation of the Shaft of the Gas Generator.

With reference to FIG. 2a , a first embodiment of the method 1000 for monitoring the coking at the dynamic seals of the turbine engine 1 will now be described.

This method utilizes a first indicator which is the deceleration of the rotation of the shaft of the gas generator, during a self-rotation phase of the shaft. Self rotation takes place during a stopping phase of the turbine engine, when the shaft of the gas generator continues its rotation by its sole inertia but is no longer driven into rotation by another element.

During this step, the speed of rotation of the shaft of the gas generator is decreasing, but the deceleration may be more or less significant depending on the degree of coking at the dynamic seals. Indeed, the more the dynamic seals are coked, the more there exists friction between the injection manifold and the injection wheel, which slows down the relative movement between both of these elements.

Therefore, deceleration is more significant in the case of significant coking.

Further, this impact of the friction on the slowing down is in proportion larger under low speed conditions than with other factors having an influence on the slowing down such as aerodynamic friction, which, themselves, depend on the speed of rotation and are therefore in proportion less significant under low speed conditions.

Therefore, the study of the deceleration of the shaft 11 under low speed conditions provides an indication on the degree of coking at the dynamic seals.

The method therefore comprises a step 1100 for measuring a speed of rotation of the shaft of the gas generator of the turbine engine with the sensor 54, during a self-rotation phase of the shaft.

With reference to FIG. 3a , the deceleration of the shaft of the gas generator is illustrated between a speed of rotation of 3,000 rpm and a speed of 600 rpm for different uses of a turbine engine, the first measurement and the last measurement having been read out with a gap of about 250 uses.

The slope of the speed of rotation is higher in absolute value for the last use, for which the amount of coke in the dynamic seals is larger.

Referring back to FIG. 2a , the method then comprises a step 1200 for determining, from the time-dependent change in the acquired speed of rotation, a degree of coking at the dynamic seals.

Indeed, as the speed of rotation has been read out at a frequency greater than 1 or 2 Hz during a deceleration phase of the shaft, it is possible to determine its slope, i.e. the deceleration of the shaft, between two determined speed values.

Herein before, it was indicated that the friction phenomena resulting from coking are more visible under low speed conditions. Therefore, speed values between which a deceleration is calculated comprise a first speed comprised between 1,000 and 2,500 revolutions per minute, preferably equal to 1,000 revolutions per minute, and a second speed of rotation comprised between 500 and 1,000 revolutions per minute, preferably equal to 700 revolutions per minute.

The processing unit therefore calculates the slope between both of these speeds during a step 1210. It may then, during a step 1220, infer the degree of coking at the dynamic seals in several ways.

According to a first embodiment, during step 1221, the processing unit compares the slope of the speed of rotation at one or several predetermined thresholds, corresponding to one or several determined degrees of coking; for example a degree of coking may correspond to a number of uses of the turbine engine before the gas generator is blocked.

The threshold may be established according to a large number of parameters depending on the turbine engine and on its conditions of use.

According to a second embodiment, during step 1222, the processing unit compares the value of the slope with an initial determined value in the same way during a first use or a first putting of the turbine engine into operation. The processing unit may calculate the difference between both slope values and compare this difference with a predetermined threshold so as to infer therefrom, as previously, a degree of coking at the seals.

Finally, according to a third embodiment, during a step 1223, the processing unit recovers calculated deceleration data under identical conditions and stored in the memory 52 and determines a changing rate of said deceleration depending on the use of the turbine engine, for example depending on a number of uses of the turbine engine (number of starts).

With reference to FIG. 3b , a time-dependent change, depending on the use of the turbine engine, from the average value of the deceleration between 3,000 and 1,000 rpm is illustrated. It is seen that the slope of this time-dependent change also tends to increase, i.e. the deceleration increases more and more gradually as the degree of coking at the seals becomes significant.

Therefore, the step 1223 comprises the measurement of a changing rate of the deceleration calculated according to the use of the turbine engine, and comparing this changing rate with a predetermined threshold.

Monitoring a Degree of Coking at the Dynamic Seals by the Current Consumed by the Starter and by the Voltage on its Terminals.

With reference to FIG. 2b , another embodiment of the method 1000 for monitoring a degree of coking at the dynamic seals is illustrated. In this embodiment, a first step 1500 comprises the measurement of the current consumed by the starter and of the voltage on its terminals, during the phase for initiating rotation of the shaft of the gas generator by the starter, during the starting of the turbine engine.

Indeed, during this step, the starter may be considered as a DC current motor and it may therefore be considered that the torque of the electric motor is proportional to the current consumed by this motor, and that the speed of rotation of the electric motor is proportional to the voltage of the motor.

The following equations are therefore obtained:

Tq_(m) = K₁ ⋅ I_(m) $\omega_{s} = \frac{V_{m}}{K_{1}}$ Wherein:

-   -   Tq_(m) is the torque of the electric motor,     -   K₁ is a constant,     -   I_(m) is the current consumed by the electric motor,     -   ω_(s) is the speed of rotation of the starter.

The torque of the electric motor compensates for the resistive torque of the shaft of the gas generator while increasing its speed of rotation. Tq _(m) =Tq _(r) +J·{dot over (ω)} Wherein:

-   -   Tq_(r) is the resistive torque of the shaft of the gas generator         on the shaft of the starter,     -   J is the inertia of the load on the shaft of the starter, and     -   ({dot over (ω)}) is the time derivative of ω_(s), i.e. the         acceleration of the shaft of the starter.

The increase in the resistive torque may be seen through the time-dependent change of the current and of the voltage on the terminals of the electric motor i.e.

the starter.

${Tq}_{r} = {{K_{1} \cdot I_{m}} - {J \cdot \frac{{\overset{.}{V}}_{m}}{K_{1}}}}$

A representative datum of the resistive torque of the shaft of the gas generator, which is homogenous with a current, may therefore be calculated as follows: imageTq _(r) =I _(m) −α·{dot over (V)} _(m)+offset Wherein:

-   -   imageTq_(r) is a representative datum of the resistive torque of         the shaft of the gas generator, obtained from the current I_(m)         consumed by the starter and from the voltage V_(m) of its         terminals,     -   I_(m) is the average value of the current consumed by the         electric motor during the phase for initiating the rotation of         the shaft of the gas generator of the starter.     -   {dot over (V)}_(m) is the average slope of V_(m) during the         phase for initiating rotation of the shaft of the gas generator         by the starter,     -   a is a constant defined so that imageTq_(r)=offset for the first         measurement point, i.e. that the initial resistive torque is         considered to be negligible.     -   offset is a constant used for obtaining an always positive value         of the torque in spite of the dispersion.

The step for measuring the current and the voltage on the terminals of the starter is therefore followed by a step 1600 for determining, from these measurements, the degree of coking at the dynamic seals, by calculating during a step 1610 from the previous equations, the datum imageTq_(r) representative of the resistive torque of the shaft of the gas generator.

The current and voltage measurements are conducted with the measurement device 55, the measuring frequency of which is advantageously greater than 10 Hz.

The inference of the coking condition at the dynamic seals 1620 may be achieved in different ways.

According to a first embodiment 1621, the value of the datum imageTq_(r), which is, as the case may be, its average value over the initiation period, may be compared with one or several predetermined thresholds, corresponding to one or several determined degrees of coking; for example a degree of coking may correspond to a number of uses of the turbine engine before the gas generator is blocked.

According to an alternative embodiment 1622, the processing unit compares the representative datum of the torque with an initial value determined during a first use or during a first setting into operation of the turbine engine. The processing unit may calculate the difference between both values and compare this difference with a predetermined threshold in order to infer therefrom, as previously, a degree of coking at the seals.

Finally, according a third embodiment, during a step 1623, the processing unit recovers data imageTq₃ regularly calculated under identical conditions and stored in the memory 52 and determines a changing rate in said datum depending on the number of uses of the turbine engine.

With reference to FIG. 4, a time-dependent change is illustrated depending on the use of the turbine engine, of the value of the image imageTq_(r) of the resistive torque of the shaft of the gas generator. It is seen that the slope of this change also tends to increase, i.e. the resistive torque of the shaft increases more and more gradually as the degree of coking at the seals becomes significant.

Therefore, the step 1623 comprises the measurement of a changing rate of variation of the image imageTq_(r) depending on the use of the turbine engine, and the comparison of this variation rate with a predetermined threshold.

The Use of Several Indicators for Monitoring Coking

Both indicators described herein before may be used simultaneously for corroborating or specifying the information on the degree of coking at the dynamic seals.

As an indicator of deceleration of the shaft of the gas generator is measured during a phase for stopping the turbine engine, while the indicator on the resistive torque of the shaft is measured during a starting phase, it is then advantageous to confront the results obtained after stopping the turbine engine.

The processing unit then compares the obtained results and provides a final indication on the degree of coking at the seals.

Further, depending on the degree of coking detected by one of the preceding methods, an alert may be triggered so as to set into place a phase for maintenance of the turbine engine. 

The invention claimed is:
 1. A method for monitoring a degree of coking at dynamic seals of a turbine engine comprising: a gas generator comprising a rotary shaft and an injection wheel mounted on said rotary shaft, the injection wheel being adapted for spraying fuel by centrifugation, and an injection manifold, adapted for conveying fuel as far as the injection wheel, the dynamic seals adapted for ensuring a seal between the injection wheel and the injection manifold, wherein the method comprises the steps of: measuring, during a self-rotation phase of the turbine engine, a speed of rotation of the rotary shaft, determining, from the time-dependent change of the thereby measured speed of rotation, a degree of coking at the dynamic seals, and selectively performing maintenance on the turbine engine based on the determined degree of coking at the dynamic seals.
 2. The monitoring method according to claim 1, wherein the step for determining the degree of coking at the dynamic seals comprises a measurement of deceleration of the rotary shaft between two speeds of rotation of the rotary shaft.
 3. The monitoring method according to claim 2, wherein the measurement of deceleration is conducted between a first speed between 1,000 and 2,500 revolutions per minute, and a second speed between 500 and 1,000 revolutions per minute.
 4. The monitoring method according to claim 2, wherein the determination of the degree of coking at the dynamic seals comprises one of the steps from among the following group: comparing the deceleration of the rotary shaft with a predetermined threshold, determining a difference between the deceleration and an initial deceleration of the turbine engine between the two speeds of rotation of the rotary shaft, and comparing the difference with a predetermined threshold, and determining a change rate associated with said deceleration depending on the use of the turbine engine, and comparing said change rate with a predetermined threshold.
 5. The monitoring method according to claim 1, applied in a turbine engine further comprising a starter, the method further comprising the steps: measuring during a phase for initiating a rotation of the rotary shaft by the starter upon starting the turbine engine, a current flowing through the starter and a voltage on terminals of the starter, determining, from the measured current and voltage, a representative datum of a resistive torque of the rotary shaft of the gas generator.
 6. The monitoring method according to claim 5, wherein the step for determining the degree of coking at the dynamic seals is achieved from the time-dependent change in the speed of rotation of the rotary shaft of the gas generator and from a value of the representative datum or time-dependent change in the representative datum of a resistive torque of the rotary shaft depending on the use of the turbine engine.
 7. A system for monitoring a coking condition at the dynamic seals of the turbine engine comprising: the gas generator, comprising the rotary shaft and the injection wheel mounted on said rotary shaft, the wheel being adapted for spraying fuel by centrifugation, the injection manifold, adapted for conveying fuel as far as the injection wheel, and the dynamic seals, adapted for ensuring the seal between the injection wheel and the injection manifold, the monitoring system being adapted for applying the method according to claim 1 and comprising: at least one sensor for the speed of rotation of the rotary shaft of the gas generator, adapted for carrying out acquisitions at a frequency greater than or equal to 2 Hz, and a processing unit, including a memory and processing means adapted for processing the acquisitions of the speed of rotation in order to determine the degree of coking at the dynamic seals.
 8. The monitoring system according to claim 7, wherein the turbine engine further comprises a starter, the monitoring system further comprising at least one device for measuring a voltage on terminals of the starter and the current flowing through the starter, said at least one device being adapted for acquiring voltage and current measurements at a frequency greater than or equal to 10 Hz.
 9. The turbine engine, comprising: the gas generator, comprising the rotary shaft and the injection wheel mounted on said shaft, the wheel being adapted for spraying fuel by centrifugation, the injection manifold, adapted for conveying fuel as far as the injection wheel, and the dynamic seals, adapted for ensuring the seal between the injection wheel and the injection manifold, wherein the turbine engine further comprises the monitoring system according to claim
 7. 